1. Field of the Invention
The present invention relates to a memory element in which data can be recorded and a memory device including the memory element.
2. Description of the Related Art
In information devices such as a computer, a DRAM capable of high speed operation and having high density is widely used as a random access memory.
However, since the DRAM has a complicated manufacturing process compared with a typical logic circuit LSI and signal processing employed in an electronic apparatus, manufacture costs increase.
Further, since the DRAM is a volatile memory in which data disappears when the power is shut off, such refreshing operation that data written therein is frequently read out to be again amplified and rewritten is needed.
Then, as a nonvolatile memory in which data does not disappear even if the power is shut off, FeRAM (Ferroelectric Random Access Memory), MRAM (Magnetic Random Access Memory) and the like are proposed, for example.
With such memory, written data can be retained for a long time without power supply.
Further, in case of those memories, a refreshing operation is unnecessary, because the memory is made nonvolatile, and it is assumed that the power consumption be reduced to that extent.
However, in the above-described nonvolatile memory, it becomes difficult to secure properties as a memory element due to a miniaturization of a memory element that constitutes each memory cell.
Therefore, it is difficult to miniaturize the element to the limit of a design rule and to the limit in a manufacturing process.
Hereupon, a memory element of a new type has been proposed as a memory having a suitable structure for miniaturization.
This memory element has a structure in which an ion conductor containing a certain metal is positioned between two electrodes.
Further, since the metal contained in the ion conductor is contained in one of the two electrodes, the metal contained in the electrode is diffused as an ion in the ion conductor when a voltage is applied between the two electrodes, and thereby an electric characteristic such as a resistance value or capacitance of the ion conductor changes.
A memory device can be made using this characteristic (for example, refer to Patent Reference 1 and Non-patent Reference 1) Specifically, the ion conductor is made of a solid solution of a chalcogenide and metal, further specifically, the ion conductor is made of a material in which Cu, Ag, Zn are solidly solved into AsS, GeS, and GeSe, and one of the two electrodes contains Cu, Ag, Zn (refer to the-above described Patent Reference 1).
Furthermore, various kinds of nonvolatile memories using a crystalline oxide material have also been proposed, and a memory in a device, for example, having a structure in which a Cr-doped SrZrO3 crystalline material is positioned between a lower electrode made of SrRuO3 or Pt and an upper electrode made of Au or Pt is proposed, where a resistance is changed reversibly when applying a voltage of a different polarity (refer to the Non-patent reference 2). However, details of the principle and so on are not clear.
[Patent Reference 1] Japanese Translation of PCT International Application No. 2002-536840
[Non-patent Reference 1] Nikkei Electronics, Jan. 20, 2003 issue (page 104)
[Non-patent Reference 2] A. Beck et al., Appl. Phys. Lett., 77, (year 2000), p. 139